An existing LED lamp typically includes a heatsink, a reflector, a diffuser plate, and a substrate having LED chips disposed thereon. Light of different colors emitted by the LED chips is synthesized into white light. Currently, it has been one of the main technical hotspots in the field of LED lighting to realize a color temperature adjustable lamp with a high color rendering index, and a method of mixing light of LEDs of different color temperatures or wavelengths is usually employed. However, it is not easy to achieve a high color rendering index, especially a high special color rendering index R9, which is required in many applications (for example, commodity exhibition). Therefore, attempts have been made to utilize a combination of phosphors or LEDs of different wavelengths. For example, in a patent application entitled “Method for Obtaining Color Temperature Adjustable White Light with High Color Rendering Index by Using Combination of White, Red and Blue LEDs” and published on Aug. 18, 2010 with a publication number CN101808451A, a blue LED chip is used to excite mixed yellow and green phosphors to produce warm white light, and then, the warm white light is mixed with a red LED light source and a blue LED light source of another wavelength to produce color temperature adjustable white light with a high color rendering index.
The above solution has several deficiencies below. 1. The coated phosphor is a mixture of a yellow phosphor and a green phosphor, a mixing ratio is not easy to control, and chrominance parameters of the finally synthesized white light are affected by an undesirable mixing ratio. Moreover, green fluorescent light is partially absorbed by the yellow phosphor, so that the excitation efficiency is reduced, the difficulty of setting the mixing ratio is further increased, and the design cost of the lamp is high. 2. Although the mixed white light is adjustable within the range of 2700K-6500K, the special color rendering index R9 is greater than 90 only, and the chromaticity difference ΔC is less than or equal to 0.01, so that the performance parameters cannot satisfy applications with high requirements. Moreover, the special color rendering index R9 is greater than 90 only within the range of 2700K-5000K, and R9 greater than 90 cannot be achieved within the entire adjustable color temperature range. 3. The two set blue LED chips have unequal peak wavelengths, increasing material selection and manufacturing costs.